Current probe designs, including vertical and cantilever probes, suffer from limitations in both design and manufacturing. Considerations include an increasing number of input/output channels, grounds, and power/electrical contact points and a decreasing array pitch size. Such limitations or concerns arise primarily because current probe designs require semiconductor solder bumps or balls to be mechanically engaged by a probe that continues travelling along a path substantially orthogonal to the surface of the semiconductor device even after initial contact. This continuing travel is often called vertical overdrive and is used to ensure each probe contacts a corresponding contact point regardless of local non-planarities, etc. Once an initial contact is established, some probe designs (e.g., cantilever probes) may provide a predictable amount of lateral motion of the probe to scratch a contacted electrical pad to improve the contact. Other probe designs (e.g., vertical probes) do not rely on scratching to ensure adequate probe contact, rather they rely on forming an indentation at the surface of the targeted electrical structure.
Testing solder bumps and solder balls on a semiconductor device may be challenging for both probe configurations, especially when the surface available for testing is substantially semi-spherical. Should a tip of a cantilever probe engage with a solder bump or a solder ball at a trailing edge of the spherical surface (e.g., a location substantially mid-way between the apex and the equator) a local slope may prevent the probe tip from effectively scratching the spherical surface, resulting in the probe tip sliding and straying off the bump. The sliding or straying may also be referred to as scooting. Such scooting or straying in an X and/or Y axis may also be more prevalent when shorter probe shaft lengths are used. In another scenario, a probe tip engaging with a solder bump at a leading edge of its spherical surface, digs into the bump surface rather than merely scratching it. As a result, reactive forces experienced by such probes may vary widely from an intended use, both in direction and magnitude and could lead to premature fatigue and failure of the probes.
Other significant challenges pertain to local non-planarity (height differences) of the individual solder bumps and a leveling of the semiconductor chip, etc. To account for such variations in planarity, vertical or cantilever probes may be designed to accommodate a wide range of vertical overdrive values to ensure a reliable electrical contact across the semiconductor chip (those probes that make physical contact with their respective solder bump need to absorb an amount of overdrive as the probe card continues traveling towards the semiconductor chip to allow other probes to eventually make contact with their respective solder bumps). However, in-plane movements along the shank of the probe itself invariably accompany any vertical tip motion. As the pitch between solder bumps grows smaller, so does the real-estate and a volume of space available for each individual probe. Consequently, an amount of lateral movement of a probe before any location along the probe shank engages mechanically with its direct neighbor solder bump shrinks accordingly. Moreover, as the space allocated for each probe shrinks, it becomes increasingly difficult to construct a mechanical design that allows for large overdrives while maintaining stress levels at any point along the probe below the material maximum yield stress.
As discussed herein, vertical and cantilever probes face a variety of handicaps. Probes are required to provide a vertical overdrive sufficient to ensure desired electrical and mechanical contact with semiconductor devices of increasingly smaller pitches. While also restricting a total volume of material allocated to the probe itself to absorb stresses during operation. Lastly, higher amounts of vertical overdrive sometimes required to guarantee good electrical and mechanical contact at every point on a semiconductor array (e.g., to deal with local non-planarities) may also lead to premature wear or fatigue.